Steering equipment for assisting a driver to steer an automobile is well known in the art. In conventional steering assemblies, the operator controls the direction of the vehicle with the aid of a steering wheel. This wheel is mechanically connected, usually through a gear assembly to the roadwheels. To aid the operator, many systems utilize an auxiliary system to generate a force that is transmitted to a steering gear assembly. The additional force reduces the effort required by the operator in changing the direction of the vehicle. Typically, this auxiliary force is generated by either a hydraulic drive or an electric motor. Because the steering wheel is connected directly to the roadwheels, the resulting mechanical assembly that provides the connection can be quite complicated and expensive to produce. One advantage in having a direct connection is that the operator receives tactile feedback through the steering wheel. For example, if the vehicle changes directions while it is moving, the operator will feel resistance in the steering wheel.
For Steer-by-wire control systems, tactile feedback may be provided to the operator by generating feedback forces in a hand wheel system that includes an actuator. Two methods have been considered for converting the sensed road forces back to the driver. The first method is direct, and simply commands the sensed forces to the Hand Wheel actuator to provide the road resistance to the driver. The advantage of this method is that the driver (almost) instantaneously feels the road forces. But, the resulting steering feel to the driver will also be sensitive to changes in the system or component variations. The second method also utilizes a road force sensor, but in a feedback loop with a torque sensor signal to generate an error signal. The advantage of this method is its insensitivity to variations (and or disturbances) in the hand wheel system. Unfortunately, to ensure adequate tactile feedback of road forces, the loop gain generally needs to be quite high, thereby making the system potentially prone to instability or susceptible to noise. Moreover, the desired road feel to the operator is commonly very subjective and a function of individual vehicle characteristics and operator taste.
Therefore, is it considered advantageous to provide a steering control system that provides customizable tactile feedback to the operator allowing for user configurable handling and response characteristics, while maintaining a system that is less sensitive to induced disturbances, but avoids instability and noise susceptibility.
A steer-by-wire control system comprising a master control system, a road wheel system, and a hand wheel system is disclosed. The road wheel system is connected to the master control system and includes a road wheel position sensor to produce and transmit a road wheel position and a rack force sensor to produce and transmit a rack force signal. The hand wheel system is connected to the master control system and the road wheel system and includes a hand wheel position sensor to produce and transmit a hand wheel position signal and a torque sensor to produce and transmit a hand wheel torque signal. The steer-by-wire system also includes a vehicle speed sensor for producing a vehicle speed signal, where the vehicle speed sensor is connected to at least one of the master control system, the hand wheel system, and road wheel system. In addition a hand wheel actuator configured to receive commands from the hand wheel system and a road wheel actuator configured to receive commands from the road wheel system are utilized. The hand wheel system and road wheel system each include a configurable control topology.